Evelo Biosciences (EVLO) 10-Q 31 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 30, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	EVLO
Entity Registrant Name	Evelo Biosciences, Inc.
Entity Central Index Key	1,694,665
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		31,720,051

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 114,311	$ 38,246
Prepaid expenses and other current assets	876	531
Total current assets	115,187	38,777
Property and equipment, net	4,429	3,496
Other assets	2,697	1,515
Total assets	122,313	43,788
Current liabilities:
Accounts payable	1,367	1,411
Accrued expenses	2,950	2,199
Other current liabilities	300	229
Total current liabilities	4,617	3,839
Noncurrent liabilities:
Long-term debt	14,719	9,966
Deferred rent, net of current portion	1,023	478
Other noncurrent liabilities	701	526
Total liabilities	21,060	14,809
Convertible preferred stock:
Convertible preferred stock, $0.001 par value; 91,543,762 and 66,311,563 shares authorized as of March 31, 2018 and December 2017, respectively; 91,315,295 and 65,833,096 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively; aggregate liquidation preference of $174,612 and $89,975 as of March 31, 2018 and December 31, 2017, respectively	165,778	83,702
Stockholder's deficit:
Common stock, $0.001 par value, 30,963,471 and 23,780,338 shares authorized at March 31, 2018 and December 31, 2017, respectively; 4,170,248 and 4,138,483 shares issued and 3,943,929 and 3,880,607 shares outstanding at March 31, 2018 and December 31, 2017, respectively	4	4
Additional paid-in capital	2,406	1,684
Accumulated deficit	(66,935)	(56,411)
Total stockholders' (deficit) equity	(64,525)	(54,723)
Total liabilities, convertible preferred stock and stockholders' (deficit) equity	$ 122,313	$ 43,788

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	91,543,762	66,311,563
Convertible preferred stock, shares issued	91,315,295	65,833,096
Convertible preferred stock, shares outstanding	91,315,295	65,833,096
Convertible preferred stock, liquidation preference	$ 174,612	$ 89,975
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	30,963,471	23,780,338
Common stock, shares issued	4,170,248	4,138,483
Common stock, shares outstanding	3,943,929	3,880,607

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating expenses:
Research and development	$ 7,143	$ 3,846
General and administrative	3,282	1,362
Total operating expenses	10,425	5,208
Loss from operations	(10,425)	(5,208)
Other (expense) income:
Interest income (expense), net	46	(72)
Other expenses	(121)	(90)
Other (expense) income, net	(75)	(162)
Net loss	(10,500)	(5,370)
Convertible preferred stock dividends	(2,417)	(1,225)
Net loss attributable to common stockholders	$ (12,917)	$ (6,595)
Net loss per share attributable to common stockholders, basic and diluted	$ (3.29)	$ (1.81)
Weighted average number of shares outstanding, basic and diluted	3,922,152	3,651,833

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (10,500)	$ (5,370)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	652	203
Depreciation expense	585	163
Change in fair value of warrant and debt derivative liability	121	90
Non-cash interest expense	17	13
Changes in assets and liabilities:
Prepaid expenses and other current assets	(345)	(114)
Accounts payable	(44)	89
Accrued expenses and other current liabilities	653	524
Other liabilities	545	45
Net cash used in operating activities	(8,316)	(4,357)
Investing activities
Purchases of property and equipment	(1,000)	(151)
Net cash used in investing activities	(1,000)	(151)
Financing activities
Net Proceeds from the issuance of convertible preferred stock	81,340	32,452
Net proceeds from the issuance of long-term debt	4,975
Payment of deferred offering costs	(970)
Proceeds from the exercise of stock options and restricted common stock	36	30
Net cash provided by financing activities	85,381	32,482
Net increase in cash, cash equivalents and restricted cash	76,065	27,974
Cash, cash equivalents and restricted cash - beginning of period	39,746	15,786
Cash, cash equivalents and restricted cash - end of period	115,811	43,760
Supplemental disclosure of cash flow information
Cash paid for interest	143	100
Noncash investing and financing activities
Accretion of convertible preferred stock		23
Accrued non-cash deferred offering costs	216
Issuance of warrants in connection with long-term debt facility	89
Property and equipment additions in accounts payable and accrued expenses	$ 602	$ 90

Organization and Basis of Prese

Organization and Basis of Presentation	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Evelo Biosciences, Inc. (“the Company”) is a biotechnology company which was incorporated in Delaware on May 6, 2014. The Company focuses on the development of monocolonal microbials, which are designed to act on the gut-body The Company is devoting substantially all of its efforts to research and development and raising capital. The Company has not generated any revenue related to its primary business purpose to date . The Company has funded its operations from the issuance of convertible notes, convertible preferred stock, common stock and debt financing. At March 31, 2018, the Company had cash and cash equivalents of $114.3 million and an accumulated deficit of $66.9 million. In February and March 2018, the Company raised $81.5 million in Series C convertible preferred stock. Additionally, in February 2018, the Company drew down its additional $5.0 million of borrowing capacity which was available under the current debt facility. On April 27, 2018, the Company filed an amended and restated certificate of incorporation with the Secretary of State of the State of Delaware, to effect a 1-for-4.079 On May 11, 2018, the Company completed an initial public offering (the “IPO”) of 5,312,500 shares of its common stock for aggregate gross proceeds of $85.0 million. The Company received approximately $75.9 million in net proceeds after deducting underwriting discounts and commissions and other estimated offering expenses payable by the Company. Offering costs incurred through March 31, 2018 are recorded in other assets on the Company’s condensed consolidated balance sheet. Upon closing of the IPO, all of the outstanding shares of convertible preferred stock automatically converted into 22,386,670 shares of common stock at the applicable conversion ratio then in effect (see Note 13). Based on the Company’s current operating plan, the Company believes that its cash and cash equivalents at March 31, 2018 together with the net proceeds from its IPO will be sufficient to fund operations and capital expenditures into the second half of 2020. The continued viability of the Company beyond that point is dependent on its ability to continue to raise additional capital to finance its operations. There can be no assurance that the Company will be able to obtain sufficient capital to cover its costs on acceptable terms, if at all.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standard Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2017 and notes thereto, included in the Company’s Form S-1/A Principles of Consolidation The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned, controlled subsidiary, Evelo Biosciences Security Corporation. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation. Subsequent Event Considerations The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. The Company has evaluated all subsequent events and determined that there are no material recognized or unrecognized subsequent events requiring disclosure, other than those disclosed in this Quarterly Report on Form 10-Q. Emerging Growth Company Status We are an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, and we may take advantage of reduced reporting requirements that are otherwise applicable to public companies. We may take advantage of these exemptions until we are no longer an emerging growth company. Section 107 of the JOBS Act provides that an emerging growth company can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. We have elected to use the extended transition period for complying with new or revised accounting standards; and as a result of this election, our financial statements may not be comparable to companies that comply with public company effective dates. We may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of this offering or such earlier time that we are no longer an emerging growth company. We would cease to be an emerging growth company if we have more than $1.07 billion in annual revenue, we have more than $700.0 million in market value of our stock held by non-affiliates Form 10-K), non-convertible Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ (deficit) equity that are excluded from net loss. For the three months ended March 31, 2018 and 2017, comprehensive loss was equal to net loss. Cash, Cash Equivalents and restricted cash Cash equivalents are comprised of highly liquid investments that are readily convertible into cash with original maturities of three months or less. Cash and cash equivalents include cash held in banks and amounts held in money market funds. Cash equivalents are stated at cost, which approximates market value. The Company’s restricted cash consists of restricted cash in connection with building leases for the Company’s office and laboratory premises. Restricted cash totaled $1.5 million at both March 31, 2018 and December 31, 2017 and is classified within the other assets on the accompanying condensed consolidated balance sheet. The following reconciles cash, cash equivalents and restricted cash as of March 31, 2018 and December 31, 2017, as presented on our statements of cash flows to their related balance sheet accounts (in thousands): March 31, December 31, 2018 2017 Cash and cash equivalents: Cash $ 89,215 $ 13,204 Money Market Funds 25,096 25,042 Total cash and cash equivalents 114,311 38,246 Restricted cash 1,500 1,500 Cash, cash equivalents and restricted cash $ 115,811 $ 39,746 Fair Value of Financial Instruments ASC 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly; and • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. An entity may choose to measure many financial instruments and certain other items at fair value at specified election dates. Subsequent unrealized gains and losses on items for which the fair value option has been elected will be reported in earnings. The Company did not elect to measure any additional financial instruments or other items at fair value. Deferred Initial Public Offering Costs Deferred public offering costs, which primarily consist of direct, incremental legal and accounting fees related to the IPO, were capitalized within other assets as of March 31, 2018. The Company incurred $1.2 million in IPO fees recorded as deferred offering costs as of March 31, 2018. This amount is included in other assets and will be offset against the proceeds upon completion of the IPO. Recently Adopted Accounting Pronouncements In March 2016, the FASB issued ASU 2016-09, 2016-09”). 2016-09 non-public In May 2017, the FASB issued ASU 2017-09, 2017-09”), non-public Accounting Pronouncements Issued and Not Adopted as of March 31, 2018 In May 2014, the FASB issued ASU No. 2014-09, 2014-09”), 2016-12 2016-12”), 2014-09 non-public 2014-09, In February 2016, the FASB issued ASU 2016-02, 2016-02”), right-of-use non-public 2016-02 2016-02

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value as of March 31, 2018 and December 31, 2017 (in thousands): Description March 31, 2018 Active Markets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Assets: Money market funds $ 25,096 $ 25,096 $ — $ — Total $ 25,096 $ 25,096 $ — $ — Liabilities: Debt Derivative $ 175 $ — $ — $ 175 Preferred Stock Warrant Liability 610 — — 610 Total $ 785 $ — $ — $ 785 Description December 31, 2017 Active Markets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Assets: Money market funds $ 25,042 $ 25,042 $ — $ — Total $ 25,042 $ 25,042 $ — $ — Liabilities: Preferred Stock Warrant Liability $ 424 $ — $ — $ 424 Total $ 424 $ — $ — $ 424 As part of the February 2018 debt drawdown, the Company’s loan and security agreement was amended to include the payment of a $0.3 million success fee to the financial institution in the event of a liquidation event, including initial public offering. The success fee represents an embedded derivative which the Company has bifurcated from the debt arrangement and carried at fair value. The debt derivative is considered a Level 3 liability, since their fair value measurements are based, in part, on significant inputs not observed in the market and reflect the Company’s best estimate of the probability of an IPO. The Preferred Stock Warrant Liabilities (the Warrants) relate to warrants to purchase convertible preferred stock issued by the Company in connection with entering into debt facility transactions from 2015 through 2018 as well as assuming warrants to purchase convertible preferred stock in connection with the acquisition of Epiva. These Warrants are considered a Level 3 liability since their fair value measurements are based, in part, on significant inputs not observed in the market and reflect the Company’s assumptions as to the fair value of the underlying convertible preferred stock and the expected volatility of the Company’s convertible preferred stock, as well as estimates regarding the number of shares that the Warrants will be exercisable for. The estimated fair value of the Warrants was determined using the Black-Scholes option-pricing model. A significant input to the fair value of the Warrants is the fair value of the Series A Preferred Stock, Series A-1 A-3 non-current March 31, 2018 December 31, 2017 Risk-free interest rate 2.3-2.4 % 2.4-2.5 % Expected dividend yield — % — % Expected term (in years) 7.6-9.9 7.9-8.6 Expected volatility 81-82 % 81-82 % Fair value of preferred stock $ 2.92 – 3.08 $ 2.41 – 2.56 The following table provides a roll-forward of the fair value of the warrant and debt derivative liability measured at fair value on a recurring basis using Level 3 significant unobservable inputs (in thousands): Level 3 Liabilities Balance at December 31, 2017 424 Issuance of embedded derivative instrument 150 Change in fair value of derivative instrument included in other income (expense), net 25 Issuance of warrants to purchase convertible preferred stock 89 Change in fair value of warrant liability, included in other income (expense), net 97 Balance at March 31, 2018 $ 785 The estimated fair value of long-term debt approximates its carrying value as the effective interest rate approximates market rates. The fair value of long-term debt, which may differ from its carrying value, is determined by market interest rates from debt arrangements which are observed in market trading which are similar to the Company’s arrangement and are considered a Level 2 input.

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	4. Property and Equipment, Net Property and equipment consists of the following (in thousands): March 31, December 31, 2018 2017 Property and equipment: Lab equipment $ 4,051 $ 3,189 Leasehold improvements 1,356 1,334 Furniture and fixtures 352 217 Computers and software 100 77 Office equipment 9 9 Construction-in-process 575 99 Property and equipment 6,443 4,925 Less: accumulated depreciation (2,014 ) (1,429 ) Property and equipment, net $ 4,429 $ 3,496 The Company recognized $0.6 million and $0.2 million of depreciation expense for the three months ended March 31, 2018 and 2017, respectively.

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consist of the following (in thousands): March 31, December 31, 2018 2017 Accrued external research and development expenses $ 1,320 $ 715 Accrued payroll and related expenses 757 256 Accrued professional fees 743 1,081 Accrued other 130 147 Total accrued expenses $ 2,950 $ 2,199

Loan and Security Agreement

Loan and Security Agreement	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Loan and Security Agreement	6. Loan and Security Agreement In November 2015, the Company entered into a loan and security agreement with a financial institution. The arrangement allowed the Company to borrow up to $4.0 million and, if certain criteria were met, to borrow up to an additional $1.5 million. The Company drew $4.0 million under the facility in the first half of 2016 and repaid these amounts in 2016. In connection with this arrangement, the Company issued a warrant that was originally exercisable into 100,000 shares of Series A Preferred Stock. The warrant was initially recorded at fair value and subsequently marked-to-market In connection with the acquisition of Epiva, the Company assumed Epiva’s credit facility (the “Credit Facility”) and the related $3.0 million of outstanding debt. Subsequent to the acquisition, the Company amended the Credit Facility to allow the Company to borrow up to $15.0 million, including the $3.0 million that was outstanding on the modification date and extending the maturity to August 15, 2020. During 2016, the Company borrowed an additional $7.0 million, bringing the total amounts outstanding as of December 31, 2016 and 2017 to $10.0 million. Under the terms of the Credit Facility the Company is required to make interest only payments through August 15, 2018. Upon the expiration of the interest only period, amounts borrowed will be repaid over 24 equal monthly payments of principal plus interest accrued through August 15, 2020. The amounts outstanding under the facility have an interest rate of the higher of (i) prime plus 0.25% or (ii) 3.75% per annum. The loan is secured by a lien on all Company assets, excluding intellectual property. In February 2018, the Company drew the additional $5.0 million available under the Credit Facility. This resulted in an increase to the interest rate to the higher of (i) prime plus 0.25% or (ii) 4.50% per annum. The interest only payment period was extended through to August 15, 2019. Upon the expiration of the interest only period, amounts borrowed will be repaid over 24 equal monthly payments of principal plus interest accrued through August 15, 2021. As such, the entire debt obligation has been classified as long-term on the Company’s consolidated balance sheet. The Company may prepay the outstanding loan at its option with a prepayment fee of 2% of principal amount if prepayment is made before August 15, 2018 or 0.5% if the prepayment is made between August 15, 2018 and August 15, 2019. In conjunction with the February 2018 drawdown, the Company issued a warrant to purchase up to 34,722 shares of the Company’s Series B preferred stock at an exercise price of $1.80 per share. As part of the February 2018 drawdown, the loan and security agreement was amended to include the payment of a $0.3 million success fee to the financial institution in the event of a liquidation event, including initial public offering. The success fee represents an embedded derivative which the Company has bifurcated from the debt arrangement and carried at fair value as discussed in Note 3. The Company has the following minimum aggregate future loan payments at March 31, 2018 (in thousands): Twelve month period ending March 31, Amount 2019 $ 713 2020 5,342 2021 7,827 2022 2,843 Total minimum payments $ 16,725 Less amounts representing interest and discount (2,006 ) Less current portion — Long-term debt, net of current portion $ 14,719 The Credit Facility contains negative covenants restricting the Company’s activities, including limitations on cash deposits, dispositions, mergers or acquisitions, incurring indebtedness or liens, paying dividends or making investments and certain other business transactions. There are no financial covenants associated with the agreement. The obligations under the agreement are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in the Company’s business, operations or financial or other condition. The Company has determined that the risk of subjective acceleration under the material adverse events clause is remote and therefore has classified the outstanding principal in non-current Interest expense for the three months ended March 31, 2018 and, 2017 was $0.2 million and $0.1 million, respectively.

Research and Development Agreem

Research and Development Agreements	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Research and Development Agreements	7. Research and Development Agreements Research and development costs are expensed in the period incurred. Research and development expenses consist of both internal and external costs such as payroll, consulting, and manufacturing costs associated with the development of the Company’s product candidates. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. The Company has and may continue to acquire the rights to develop and commercialize new product candidates from third parties. The upfront payments to acquire license, product or rights, as well as any future milestone payments, are immediately recognized as research and development expense provided that there is no alternative future use of the rights in other research and development projects. Any milestone payments made for Intellectual Property after regulatory approval, or that have alternative future use, are capitalized and amortized. Mayo Foundation for Medical Education and Research On June 10, 2016, the Company entered into a Research and License Agreement, (the “2016 Mayo License Agreement”) with Mayo Foundation for Medical Education and Research (“Mayo”). Under the Mayo License Agreement, Mayo was entitled to certain participation rights in connection with the issuance and sale of Series B Preferred Stock. The 2016 Mayo License Agreement allowed Mayo to purchase shares at the same price paid as other investors and is considered to be a fair value contract. In 2017, Mayo purchased 1,666,667 shares of Series B Preferred Stock at $1.80 per share. Also pursuant to the 2016 Mayo License Agreement, Mayo received 490 shares of common stock upon the completion of certain project milestones as well as warrants to purchase common stock (the “Mayo Warrants”) exercisable for 18 shares and 116 shares of common stock upon the completion of certain additional project milestones. The Mayo Warrants were fully vested and expensed in 2016. On April 9, 2018, Mayo Foundation exercised its warrant and was issued 134 shares of common stock. On August 6, 2017, the Company and Mayo entered into a license agreement (“2017 Mayo License Agreement”). Under the 2017 Mayo License Agreement, Mayo granted the Company (i) an exclusive, worldwide, sublicensable license under Mayo’s rights to certain intellectual property and microbial strains (ii) a non-exclusive, know-how, University of Chicago On March 10, 2016, the Company and the University of Chicago entered into a patent license agreement (“2016 University of Chicago Agreement”). Under the 2016 University of Chicago Agreement, the University of Chicago granted the Company (i) an exclusive, royalty-bearing and sublicensable license under the Licensed Patents and (ii) a non-exclusive, University of Surrey On February 15, 2018, the Company and the University of Surrey entered into a Clinical Trial Agreement for an industry sponsored research agreement (the “Surrey Agreement”), in which the University of Surrey agreed to conduct a proof of concept clinical trial of EDP1066 in healthy volunteers and in patients with mild to moderate psoriasis and atopic dermatitis. In connection with the Surrey Agreement the Company agreed to a total consideration of £1.1 million with 10% due on the effective date of the agreement. The remaining total consideration will be due upon the completion of the milestones outlined in the agreement. Biose Industrie On February 15, 2018, the Company entered into an Exclusivity and Commitment Agreement with Biose Industrie (“Biose”), a French corporation, in which Biose agrees to exclusively manufacture certain microbial biotherapeutic products for the Company and reserve agreed upon manufacturing resources to conduct manufacturing runs for such products. Under the terms of this agreement, the Company agreed to annual fees in the mid-six

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Lease Obligations In January 2018, the Company entered into an operating sublease arrangement to lease approximately 40,765 square feet for its office and research development space at 620 Memorial Drive, Cambridge, MA 02139 from February 2018 to September 2025. The Company maintains additional separate operating leases for office and laboratory space that expire in 2018 and 2020, respectively. The leases and sublease require security deposits, which the Company has met with letters of credit from a financial institution that are secured with cash on deposit. The Company recorded rent expense of $0.7 million and $0.3 million for the three months ended March 31, 2018 and 2017, respectively. The minimum aggregate future lease commitments at March 31, 2018, are as follows (in thousands). Twelve month period ending March 31, Amount 2019 $ 3,338 2020 3,304 2021 2,989 2022 2,995 2023 3,085 Thereafter 8,112 $ 23,823 Compensation Commitment The Company entered into a compensation arrangement with a consultant during May 2017 which provided for a future cash and a variable share payment in exchange for services. The services were completed in August 2017 and in January 2018, the Company settled the arrangement by making a cash payment and issuing 250,000 shares of Series B Preferred Stock. Accordingly, the Company recorded the fair value of the underlying shares totaling $0.7 million, which was substantially all recorded as accrued expense at December 31, 2017.

Stockholders' (Deficit) Equity

Stockholders' (Deficit) Equity and Convertible Preferred Stock	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Stockholders' (Deficit) Equity and Convertible Preferred Stock	9. Stockholders’ (Deficit) Equity and Convertible Preferred Stock Convertible Preferred Stock In February and March 2018, the Company issued a total of 25,232,199 shares of Series C Preferred Stock at purchase price of $3.23 for gross proceeds $81.5 million under the same terms as the Series B Preferred Stock. In 2017, the Company issued a total of 27,777,778 shares of Series B Preferred Stock at purchase price of $1.80 for gross proceeds $50.0 million in four separate closings in the first half of 2017. The terms of the Series B Preferred Stock modified certain terms of the existing Series A, A-1, A-2, A-3 A-1, A-2, A-3 A-1, A-2 A-3 Upon closing of the IPO in May 2018, the Series A, Series A-1, A-2, A-3, At March 31, 2018, convertible preferred stock consisted of the following (in thousands except share and per share data): Shares Shares Issuance Carrying Liquidation Cumulative Convertible Series A Preferred 13,470,279 13,370,279 $ 0.60 $ 8,936 $ 9,866 $ 1,844 Series A-1 10,164,552 10,102,055 0.60 6,712 7,348 1,287 Series A-2 5,833,334 5,833,334 1.20 7,287 8,019 1,023 Series A-3 8,780,898 8,749,650 1.20 10,960 12,060 1,566 Series B Preferred 28,062,500 28,027,778 1.80 50,547 55,165 4,425 Series C Preferred 25,232,199 25,232,199 3.23 81,336 82,154 684 91,543,762 91,315,295 $ 165,778 $ 174,612 $ 10,829 The Series A, Series A-1, A-2, A-3, Conversion The preferred stock is convertible into common stock at any time at the option of the holder, initially on a 1-for-1 Voting The holders of the preferred stock have voting rights equivalent to the number of shares of common stock into which the preferred stock is convertible into. In addition, a majority of the preferred stockholders must approve certain items, including the approval of any dissolution, liquidation, amendment to the articles of incorporation, creation of new senior securities, payment of dividends, election of certain directors and adjusting the total number of directors, as well as other related items. Dividends Holders of shares of Series A, Series A-1, A-2, A-3 Liquidation In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or a deemed liquidation event, the holders of shares of preferred stock then outstanding are entitled to be paid out of the assets of the Company available for distribution to its stockholders, before any payment can be made to the holders of common stock, an amount per share equal to the greater of (i) the original issue price for the Series of preferred stock held plus any dividends accrued but unpaid, whether or not declared; or (ii) such amount per share as would have been paid if all shares of preferred stock had been converted to common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation event. If assets of the Company available are insufficient to pay holders of preferred stock the full amount they are entitled to, the holders of preferred stock will share ratably in any distribution of the assets available for distribution in proportion to the amounts due such holders. After the payment of all preferential amounts required to be paid to the holders of shares of preferred stock, the remaining assets of the Company will be distributed among the holders of the shares of common stock, pro rata based on the number of shares held by each such holder. Redemption Prior to the issuance of Series B Convertible Preferred Stock, all series of preferred stock became redeemable at specific dates. As such, the Company was accreting dividends on their preferred stock. Upon issuance of Series B Convertible Preferred Stock, all date certain redemption features were removed and the Company concluded that it was no longer probable that the preferred stock would become redeemable. As such, the Company stopped accreting dividends on their preferred stock in 2017. Upon certain change in control events that are outside of the Company’s control, including liquidation, sale or transfer of control of the Company, holders of the convertible preferred stock can cause its redemption. Shares of preferred stock must be redeemed by the Company at the original issue price for each series of preferred stock plus any dividends accrued but unpaid, whether or not declared, on the fifth month anniversary of such event, upon a written request from the holders of a majority of the then outstanding shares of preferred stock. This request can be made at any time before fourth month anniversary of such event. The Company classifies its convertible preferred stock outside of stockholders’ (deficit) equity as certain change in control events are outside the Company’s control.

Stock Incentive Plan

Stock Incentive Plan	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Incentive Plan	10. Stock Incentive Plan 2018 Stock Incentive Plan The Company’s board of directors adopted and the Company’s stockholders approved, effective the day prior to the first public trading date of our common stock, the 2018 Stock Incentive Plan (the “2018 Plan”), under which the Company may grant cash and equity-based incentive awards to the Company’s employees, officers, directors, consultants and advisors. Following the effectiveness of the 2018 Plan, the Company will not make any further grants under the 2015 Stock Incentive Plan (the “2015 Plan”). However, the 2015 Plan will continue to govern the terms and conditions of the outstanding awards granted under it. Shares of common stock subject to awards granted under the 2015 Plan that are forfeited, lapse unexercised or are settled in cash and which following the effective date of the 2015 Plan are not issued under the 2015 Plan will be available for issuance under the 2018 Plan. 2015 Stock Incentive Plan In 2015, the Company adopted the 2015 Stock Incentive Plan, as amended (“2015 Plan”), which originally provided for grant of incentive stock options, non-qualified The terms of stock awards agreements, including vesting requirements, are determined by the board of directors and are subject to the provisions of the 2015 Plan. The stock options granted to employees generally vest over a four-year period but may be granted with different vesting terms. Certain awards contain performance based vesting criteria and as of March 31, 2018 the Company has concluded the vesting of these awards is not probable. There are ten such awards to date. Certain options provide for accelerated vesting in the event of a change in control, as defined above. Awards granted to non-employee As of March 31, 2018 and December 31, 2017, 1,007,866 and 107,262 shares of common stock were available for future grant under the 2015 Plan. Stock-Based Stock-based compensation expense included in the Company’s statements of operations is as follows (in thousands): Three Months Ended March 31, 2018 2017 General and administrative $ 410 $ 111 Research and development 242 92 Total stock-based compensation expense $ 652 $ 203 Stock Options A summary of the stock option activity under the 2015 Plan is as follows: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life Aggregate Intrinsic Value (1) (in thousands) Options outstanding at December 31, 2017 3,179,536 $ 1.88 9.05 $ 19,803 Granted 82,367 $ 3.96 Exercised (31,765 ) $ 1.13 Canceled (2,343 ) $ 1.12 Options outstanding at March 31, 2018 3,227,795 $ 1.95 8.83 27,544 Exercisable as of March 31, 2018 679,400 $ 1.07 8.29 6,395 Vested and expected to vest as of March 31, 2018 (2) 3,227,795 $ 1.95 8.83 $ 27,544 (1) The aggregate intrinsic value of options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the ordinary shares as of the end of the period. (2) This reflects the Company’s adoption and election under ASU 2016-09 to recognize forfeitures as they occur. The Company had 2,548,395 unvested stock options outstanding as of March 31, 2018. The weighted-average fair value of options granted during the three months ended March 31, 2018 and 2017 was $7.91 and $1.75, respectively. When utilizing the Black-Scholes option-pricing model to determine the grant date fair value of stock options granted to employees as well as the vesting or re-measurement non-employees, non-employees: Employee option grants Three Months Ended March 31, 2018 2017 Risk-free interest rate 2.48 % 2.10 % Expected life (in years) 6.17 6.05 Volatility 78.2 % 82.9 % Expected dividend rate — — Fair value of common stock $ 9.67 $ 2.49 Non-employee Three Months Ended March 31, 2018 2017 Risk-free interest rate 2.53 % 2.30 % Expected life (in years) 8.79 9.29 Volatility 77.9 % 82.5 % Expected dividend rate — — Fair value of common stock $ 10.48 $ 3.06 The Company estimates the expected life of options granted based on the remaining contractual term of the option for options granted to non-employees. On January 30, 2018, the Company issued 250,000 Series B Preferred Stock to a non-employee As of March 31, 2018, total unrecognized stock-based compensation expense relating to unvested stock options was $8.8 million. This amount is subject to change as the unvested portion of the stock options granted to non-employees re-measurement Restricted Stock The Company permitted the early exercise of certain stock options prior to vesting by certain directors and officers. This practice ceased in 2017. Any shares issued pursuant to unvested options are restricted and subject to repurchase by the Company until the conditions for vesting are met. Accordingly, the Company has recorded the proceeds from the issuance of restricted stock as a liability in the consolidated balance sheets included as a component of other current and noncurrent liabilities based on the scheduled vesting dates. The amounts paid for shares purchased under an early exercise of stock options and subject to repurchase by the Company are reported in stockholders’ (deficit) equity once those shares vest. Upon termination of employment of an option holder, the Company has the right to repurchase, at the original purchase price, any unvested restricted shares. Shares Weighted- Average Price Unvested Restricted Common Stock as of December 31, 2017 257,876 $ 0.40 Vested (31,557 ) $ 0.34 Unvested Restricted Common Stock as of March 31, 2018 226,319 $ 0.38 As of March 31, 2018, the Company had $0.1 million of unrecognized stock-based compensation expense related to its employee unvested restricted stock awards which is expected to be recognized over a remaining weighted average vesting period of 1.34 years.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes On December 22, 2017, the Tax Cuts and Jobs Act (the “Act”) was enacted in the United States. The Act incorporates significant changes to U.S. corporate income tax laws including, among other things, a reduction in the statutory federal corporate income tax rate from 35% to 21%, an exemption for dividends received from certain foreign subsidiaries, a one-time As of March 31, 2018, we have not completed our accounting for the tax effects of enactment of the Act. We remeasured certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21%. The Company has no foreign earnings and therefore is not subject to transition tax. However, we are still analyzing certain aspects of the Act and refining our calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts. The provisional amount recorded related to the remeasurement of our deferred tax balance was a $11.9 million provision that was offset by a valuation allowance.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	12. Net Loss Per Share Basic and diluted net loss per common share is determined by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding during the period. The Company has computed diluted net loss per common share after giving consideration to all potentially dilutive common shares, including options to purchase common stock, restricted common stock, convertible preferred stock and warrants to purchase convertible preferred stock, outstanding during the period determined using the if-converted method, except where the effect of including such securities would be antidilutive. Because the Company has reported net losses since inception, these potential common shares have been anti-dilutive and basic and diluted loss per share have been the same. The following potentially dilutive securities have been excluded from the computations of diluted weighted-average shares outstanding as they would be anti-dilutive: Three Months Ended March 31, 2018 2017 Convertible preferred shares (as converted to common stock) 22,386,670 13,892,227 Warrant to purchase convertible preferred shares (as converted to common stock) 56,008 47,496 Unvested common stock from early exercise of options 226,319 387,033 Stock options to purchase common stock 3,227,795 1,930,941 Total 25,896,792 16,257,697

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events Initial Public Offering On April 27, 2018, the Company filed an amended and restated certificate of incorporation with the Secretary of State of the State of Delaware, to effect a 1-for-4.079 On May 11, 2018, the Company closed its initial public offering with the sale of 5,312,500 shares of common stock at a public offering price of $16.00 per share, resulting in net proceeds of $75.9 million, after deducting underwriting discounts and commissions and other estimated offering expenses payable by the Company. Upon the closing of the IPO, all of the Company’s outstanding shares of convertible preferred stock automatically converted into 22,386,670 shares of common stock at the applicable conversion ratio then in effect.

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standard Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2017 and notes thereto, included in the Company’s Form S-1/A
Principles of Consolidation	Principles of Consolidation The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned, controlled subsidiary, Evelo Biosciences Security Corporation. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation.
Subsequent Event Considerations	Subsequent Event Considerations The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. The Company has evaluated all subsequent events and determined that there are no material recognized or unrecognized subsequent events requiring disclosure, other than those disclosed in this Quarterly Report on Form 10-Q.
Emerging Growth Company Status	Emerging Growth Company Status We are an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, and we may take advantage of reduced reporting requirements that are otherwise applicable to public companies. We may take advantage of these exemptions until we are no longer an emerging growth company. Section 107 of the JOBS Act provides that an emerging growth company can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. We have elected to use the extended transition period for complying with new or revised accounting standards; and as a result of this election, our financial statements may not be comparable to companies that comply with public company effective dates. We may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of this offering or such earlier time that we are no longer an emerging growth company. We would cease to be an emerging growth company if we have more than $1.07 billion in annual revenue, we have more than $700.0 million in market value of our stock held by non-affiliates Form 10-K), non-convertible
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ (deficit) equity that are excluded from net loss. For the three months ended March 31, 2018 and 2017, comprehensive loss was equal to net loss.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and restricted cash Cash equivalents are comprised of highly liquid investments that are readily convertible into cash with original maturities of three months or less. Cash and cash equivalents include cash held in banks and amounts held in money market funds. Cash equivalents are stated at cost, which approximates market value. The Company’s restricted cash consists of restricted cash in connection with building leases for the Company’s office and laboratory premises. Restricted cash totaled $1.5 million at both March 31, 2018 and December 31, 2017 and is classified within the other assets on the accompanying condensed consolidated balance sheet. The following reconciles cash, cash equivalents and restricted cash as of March 31, 2018 and December 31, 2017, as presented on our statements of cash flows to their related balance sheet accounts (in thousands): March 31, December 31, 2018 2017 Cash and cash equivalents: Cash $ 89,215 $ 13,204 Money Market Funds 25,096 25,042 Total cash and cash equivalents 114,311 38,246 Restricted cash 1,500 1,500 Cash, cash equivalents and restricted cash $ 115,811 $ 39,746
Fair Value of Financial Instruments	Fair Value of Financial Instruments ASC 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly; and • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. An entity may choose to measure many financial instruments and certain other items at fair value at specified election dates. Subsequent unrealized gains and losses on items for which the fair value option has been elected will be reported in earnings. The Company did not elect to measure any additional financial instruments or other items at fair value.
Deferred Initial Public Offering Costs	Deferred Initial Public Offering Costs Deferred public offering costs, which primarily consist of direct, incremental legal and accounting fees related to the IPO, were capitalized within other assets as of March 31, 2018. The Company incurred $1.2 million in IPO fees recorded as deferred offering costs as of March 31, 2018. This amount is included in other assets and will be offset against the proceeds upon completion of the IPO.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In March 2016, the FASB issued ASU 2016-09, 2016-09”). 2016-09 non-public In May 2017, the FASB issued ASU 2017-09, 2017-09”), non-public Accounting Pronouncements Issued and Not Adopted as of March 31, 2018 In May 2014, the FASB issued ASU No. 2014-09, 2014-09”), 2016-12 2016-12”), 2014-09 non-public 2014-09, In February 2016, the FASB issued ASU 2016-02, 2016-02”), right-of-use non-public 2016-02 2016-02

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Reconciliation of Cash,Cash Equivalents and Restricted cash	The following reconciles cash, cash equivalents and restricted cash as of March 31, 2018 and December 31, 2017, as presented on our statements of cash flows to their related balance sheet accounts (in thousands): March 31, December 31, 2018 2017 Cash and cash equivalents: Cash $ 89,215 $ 13,204 Money Market Funds 25,096 25,042 Total cash and cash equivalents 114,311 38,246 Restricted cash 1,500 1,500 Cash, cash equivalents and restricted cash $ 115,811 $ 39,746

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value	The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value as of March 31, 2018 and December 31, 2017 (in thousands): Description March 31, 2018 Active Markets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Assets: Money market funds $ 25,096 $ 25,096 $ — $ — Total $ 25,096 $ 25,096 $ — $ — Liabilities: Debt Derivative $ 175 $ — $ — $ 175 Preferred Stock Warrant Liability 610 — — 610 Total $ 785 $ — $ — $ 785 Description December 31, 2017 Active Markets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Assets: Money market funds $ 25,042 $ 25,042 $ — $ — Total $ 25,042 $ 25,042 $ — $ — Liabilities: Preferred Stock Warrant Liability $ 424 $ — $ — $ 424 Total $ 424 $ — $ — $ 424
Summary of Assumptions in Valuing Material Warrants	The following assumptions were used in valuing the material Warrants: March 31, 2018 December 31, 2017 Risk-free interest rate 2.3-2.4 % 2.4-2.5 % Expected dividend yield — % — % Expected term (in years) 7.6-9.9 7.9-8.6 Expected volatility 81-82 % 81-82 % Fair value of preferred stock $ 2.92 – 3.08 $ 2.41 – 2.56
Roll-Forward of Fair Value of Warrant Liability Measured at Fair Value on a Recurring Basis	The following table provides a roll-forward of the fair value of the warrant and debt derivative liability measured at fair value on a recurring basis using Level 3 significant unobservable inputs (in thousands): Level 3 Liabilities Balance at December 31, 2017 424 Issuance of embedded derivative instrument 150 Change in fair value of derivative instrument included in other income (expense), net 25 Issuance of warrants to purchase convertible preferred stock 89 Change in fair value of warrant liability, included in other income (expense), net 97 Balance at March 31, 2018 $ 785

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consists of the following (in thousands): March 31, December 31, 2018 2017 Property and equipment: Lab equipment $ 4,051 $ 3,189 Leasehold improvements 1,356 1,334 Furniture and fixtures 352 217 Computers and software 100 77 Office equipment 9 9 Construction-in-process 575 99 Property and equipment 6,443 4,925 Less: accumulated depreciation (2,014 ) (1,429 ) Property and equipment, net $ 4,429 $ 3,496

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): March 31, December 31, 2018 2017 Accrued external research and development expenses $ 1,320 $ 715 Accrued payroll and related expenses 757 256 Accrued professional fees 743 1,081 Accrued other 130 147 Total accrued expenses $ 2,950 $ 2,199

Loan and Security Agreement (Ta

Loan and Security Agreement (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of Minimum Aggregate Future Loan Payments	The Company has the following minimum aggregate future loan payments at March 31, 2018 (in thousands): Twelve month period ending March 31, Amount 2019 $ 713 2020 5,342 2021 7,827 2022 2,843 Total minimum payments $ 16,725 Less amounts representing interest and discount (2,006 ) Less current portion — Long-term debt, net of current portion $ 14,719

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Minimum Aggregate Future Lease Commitments	The minimum aggregate future lease commitments at March 31, 2018, are as follows (in thousands). Twelve month period ending March 31, Amount 2019 $ 3,338 2020 3,304 2021 2,989 2022 2,995 2023 3,085 Thereafter 8,112 $ 23,823

Stockholders' (Deficit) Equit26

Stockholders' (Deficit) Equity and Convertible Preferred Stock (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Summary of Convertible Preferred Stock	At March 31, 2018, convertible preferred stock consisted of the following (in thousands except share and per share data): Shares Shares Issuance Carrying Liquidation Cumulative Convertible Series A Preferred 13,470,279 13,370,279 $ 0.60 $ 8,936 $ 9,866 $ 1,844 Series A-1 10,164,552 10,102,055 0.60 6,712 7,348 1,287 Series A-2 5,833,334 5,833,334 1.20 7,287 8,019 1,023 Series A-3 8,780,898 8,749,650 1.20 10,960 12,060 1,566 Series B Preferred 28,062,500 28,027,778 1.80 50,547 55,165 4,425 Series C Preferred 25,232,199 25,232,199 3.23 81,336 82,154 684 91,543,762 91,315,295 $ 165,778 $ 174,612 $ 10,829

Stock Incentive Plan (Tables)

Stock Incentive Plan (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock-based Compensation Expense	Stock-based compensation expense included in the Company’s statements of operations is as follows (in thousands): Three Months Ended March 31, 2018 2017 General and administrative $ 410 $ 111 Research and development 242 92 Total stock-based compensation expense $ 652 $ 203
Summary of Stock Option Activity	A summary of the stock option activity under the 2015 Plan is as follows: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life Aggregate Intrinsic Value (1) (in thousands) Options outstanding at December 31, 2017 3,179,536 $ 1.88 9.05 $ 19,803 Granted 82,367 $ 3.96 Exercised (31,765 ) $ 1.13 Canceled (2,343 ) $ 1.12 Options outstanding at March 31, 2018 3,227,795 $ 1.95 8.83 27,544 Exercisable as of March 31, 2018 679,400 $ 1.07 8.29 6,395 Vested and expected to vest as of March 31, 2018 (2) 3,227,795 $ 1.95 8.83 $ 27,544 (1) The aggregate intrinsic value of options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the ordinary shares as of the end of the period. (2) This reflects the Company’s adoption and election under ASU 2016-09 to recognize forfeitures as they occur.
Schedule of Assumptions to Used Determine Fair Value of Options Granted to Employees and Non-employees	Employee option grants Three Months Ended March 31, 2018 2017 Risk-free interest rate 2.48 % 2.10 % Expected life (in years) 6.17 6.05 Volatility 78.2 % 82.9 % Expected dividend rate — — Fair value of common stock $ 9.67 $ 2.49 Non-employee Three Months Ended March 31, 2018 2017 Risk-free interest rate 2.53 % 2.30 % Expected life (in years) 8.79 9.29 Volatility 77.9 % 82.5 % Expected dividend rate — — Fair value of common stock $ 10.48 $ 3.06
Summary of Restricted Stock Activity	Shares Weighted- Average Price Unvested Restricted Common Stock as of December 31, 2017 257,876 $ 0.40 Vested (31,557 ) $ 0.34 Unvested Restricted Common Stock as of March 31, 2018 226,319 $ 0.38

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding	The following potentially dilutive securities have been excluded from the computations of diluted weighted-average shares outstanding as they would be anti-dilutive: Three Months Ended March 31, 2018 2017 Convertible preferred shares (as converted to common stock) 22,386,670 13,892,227 Warrant to purchase convertible preferred shares (as converted to common stock) 56,008 47,496 Unvested common stock from early exercise of options 226,319 387,033 Stock options to purchase common stock 3,227,795 1,930,941 Total 25,896,792 16,257,697

Organization and Basis of Pre29

Organization and Basis of Presentation - Additional Information (Detail) $ in Thousands	May 11, 2018USD ($)shares	Apr. 27, 2018	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Cash and cash equivalents			$ 114,311		$ 38,246
Accumulated deficit			(66,935)		$ (56,411)
Additional borrowing capacity			4,975
Net Proceeds from the issuance of convertible preferred stock			$ 81,340	$ 32,452
Subsequent Event [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Reverse stock split ratio		0.2451
Subsequent Event [Member] | Common Stock [Member] | IPO [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of shares issued in transaction | shares	5,312,500
Aggregate gross proceeds from transaction	$ 85,000
Net proceeds from transaction	$ 75,900
Conversion of shares, shares converted | shares	22,386,670

Summary of Significant Accoun30

Summary of Significant Accounting Policies - Additional information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Period for issuance of non-convertible debt securities in determining the threshold value of securities issued and whether the Company will remain an emerging growth company	3 years
Restricted cash	$ 1,500,000	$ 1,500,000
Deferred offering costs	1,200,000
Maximum [Member]
Significant Accounting Policies [Line Items]
Emerging growth company, annual revenue threshold	1,070,000,000
Emerging growth company, aggregate market value of common stock held by non affiliates	700,000,000
Value of non-convertible debt securities, in excess of, that was issued during the prior three-year period, in determining whether the Company will remain an emerging growth company	$ 1,000,000,000

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash	$ 89,215	$ 13,204
Money Market Funds	25,096	25,042
Total cash and cash equivalents	114,311	38,246
Restricted cash	1,500	1,500
Cash, cash equivalents and restricted cash	$ 115,811	$ 39,746	$ 43,760	$ 15,786

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Money market funds	$ 25,096	$ 25,042
Liabilities:
Total	785	424
Debt Derivative [Member]
Liabilities:
Total	175
Preferred Stock Warrant Liability [Member]
Liabilities:
Total	610	424
Money Market Funds [Member]
Assets:
Money market funds	25,096	25,042
Active Markets (Level1) [Member]
Assets:
Money market funds	25,096	25,042
Active Markets (Level1) [Member] | Money Market Funds [Member]
Assets:
Money market funds	25,096	25,042
Unobservable Inputs (Level 3) [Member]
Liabilities:
Total	785	424
Unobservable Inputs (Level 3) [Member] | Debt Derivative [Member]
Liabilities:
Total	175
Unobservable Inputs (Level 3) [Member] | Preferred Stock Warrant Liability [Member]
Liabilities:
Total	$ 610	$ 424

Fair Value Measurements - Addit

Fair Value Measurements - Additional information (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Feb. 28, 2018	Dec. 31, 2017
Fair Value Disclosures [Line Items]
Warrants	$ 0.6		$ 0.4
Line of Credit [Member]
Fair Value Disclosures [Line Items]
Success fee		$ 0.3

Fair Value Measurements - Sum34

Fair Value Measurements - Summary of Assumptions in Valuing Material Warrants (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected dividend yield	0.00%	0.00%
Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk-free interest rate	2.30%	2.40%
Expected term (in years)	7 years 7 months 6 days	7 years 10 months 24 days
Expected volatility	81.00%	81.00%
Minimum [Member] | Convertible Preferred Stock [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of preferred stock	$ 2.92	$ 2.41
Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk-free interest rate	2.40%	2.50%
Expected term (in years)	9 years 10 months 25 days	8 years 7 months 6 days
Expected volatility	82.00%	82.00%
Maximum [Member] | Convertible Preferred Stock [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of preferred stock	$ 3.08	$ 2.56

Fair Value Measurements - Roll-

Fair Value Measurements - Roll-Forward of Fair Value of Warrant And Debt Derivative Liability Measured at Fair Value on a Recurring Basis (Detail) - Unobservable Inputs (Level 3) [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 424
Ending Balance	785
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Issuance of embedded derivative instrument and warrants to purchase convertible preferred stock	150
Change in fair value of derivative instrument and warrant liability included in other income (expense), net	25
Warrant Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Issuance of embedded derivative instrument and warrants to purchase convertible preferred stock	89
Change in fair value of derivative instrument and warrant liability included in other income (expense), net	$ (97)

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property and equipment:
Property and equipment	$ 6,443	$ 4,925
Less: accumulated depreciation	(2,014)	(1,429)
Property and equipment, net	4,429	3,496
Lab Equipment [Member]
Property and equipment:
Property and equipment	4,051	3,189
Leasehold Improvements [Member]
Property and equipment:
Property and equipment	1,356	1,334
Furniture and Fixtures [Member]
Property and equipment:
Property and equipment	352	217
Computers and Software [Member]
Property and equipment:
Property and equipment	100	77
Office Equipment [Member]
Property and equipment:
Property and equipment	9	9
Construction in Progress [Member]
Property and equipment:
Property and equipment	$ 575	$ 99

Property and Equipment, Net - A

Property and Equipment, Net - Additional information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation	$ 585	$ 163

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued external research and development expenses	$ 1,320	$ 715
Accrued payroll and related expenses	757	256
Accrued professional fees	743	1,081
Accrued other	130	147
Total accrued expenses	$ 2,950	$ 2,199

Loan and Security Agreement - A

Loan and Security Agreement - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Nov. 30, 2015
Line of Credit Facility [Line Items]
Loan and security agreement, borrowing capacity		$ 15,000,000					$ 4,000,000
Borrowing under loan and security agreement				$ 10,000,000	$ 10,000,000	$ 4,000,000
Maturity date	Aug. 15, 2021			Aug. 15, 2020
Credit facility, additional amount borrowed	$ 5,000,000				$ 7,000,000
Interest only payments end date	Aug. 15, 2019			Aug. 15, 2018
Interest expense		200,000	$ 100,000
Maximum [Member]
Line of Credit Facility [Line Items]
Credit facility, additional borrowing capacity							$ 1,500,000
Series B Preferred Stock [Member]
Line of Credit Facility [Line Items]
Number of shares called by warrants	34,722
Warrants exercise price per share	$ 1.80
Series A Preferred Stock [Member]
Line of Credit Facility [Line Items]
Number of shares called by warrants							100,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Prepayment fee before August 15, 2018	2.00%
Prepayment fee between August 15, 2018 and August 15, 2019	0.50%
Success fee	$ 300,000
Line of Credit [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Loan and security agreement, interest rate	4.50%			3.75%
Line of Credit [Member] | Prime Plus [Member]
Line of Credit Facility [Line Items]
Loan and security agreement, basis spread on interest rate	0.25%			0.25%
Epiva Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowing under loan and security agreement		$ 3,000,000

Loan and Security Agreement - S

Loan and Security Agreement - Schedule of Minimum Aggregate Future Loan Payments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Long-term debt, net of current portion	$ 14,719	$ 9,966
Line of Credit [Member]
Line of Credit Facility [Line Items]
2,019	713
2,020	5,342
2,021	7,827
2,022	2,843
Total minimum payments	16,725
Less amounts representing interest and discount	(2,006)
Less current portion	0
Long-term debt, net of current portion	$ 14,719

Research and Development Agre41

Research and Development Agreements - Additional Information (Detail) - USD ($)	Feb. 15, 2018	Aug. 06, 2017	Mar. 10, 2016	Apr. 09, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 10, 2016
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Common stock shares issued					4,170,248	4,138,483
2016 Mayo License Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Purchase of preferred stock							1,666,667
Preferred stock par value per share							$ 1.80
Common stock shares issued							490
Mayo Warrants [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Warrants to purchase of common stock exercisable							18
Number of shares of common stock upon completion							116
Mayo Warrants [Member] | Subsequent Event [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Common stock shares issued				134
2017 Mayo License Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-refundable upfront fee		$ 200,000
2017 Mayo License Agreement [Member] | Maximum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments upon achievement of certain development, regulatory, and commercial events		$ 56,000,000
2016 University of Chicago Agreement [Member] | Maximum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-refundable upfront fee			$ 500,000
Clinical Trial Agreement [Member] | University of Surrey [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total consideration under Surrey Agreement	$ 1,100,000
Percentage of consideration due	10.00%
Exclusivity and Commitment Agreement [Member] | Biose Industrie [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Exclusivity fee payable	$ 300,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	Jan. 30, 2018USD ($)shares	Jan. 31, 2018USD ($)ft²shares	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Commitment And Contingencies [Line Items]
Area of leased office and research development space | ft²		40,765
Lease term description			February 2018 to September 2025
Rent expense			$ 0.7	$ 0.3
Laboratory Space [Member]
Commitment And Contingencies [Line Items]
Operating lease, expiration year			2,020
Office Space [Member]
Commitment And Contingencies [Line Items]
Operating lease, expiration year			2,018
Series B Preferred Stock [Member] | Non Employees [Member]
Commitment And Contingencies [Line Items]
Stock issued in exchange for service | shares	250,000	250,000
Fair value of underlying shares		$ 0.7
Series B Preferred Stock [Member] | Non Employees [Member] | General and Administrative [Member]
Commitment And Contingencies [Line Items]
Fair value of underlying shares	$ 0.7		$ 0.1		$ 0.7

Commitments and Contingencies43

Commitments and Contingencies - Schedule of Minimum Aggregate Future Lease Commitments (Detail) $ in Thousands	Mar. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,019	$ 3,338
2,020	3,304
2,021	2,989
2,022	2,995
2,023	3,085
Thereafter	8,112
Operating leases, Future minimum payments due	$ 23,823

Stockholders' (Deficit) Equit44

Stockholders' (Deficit) Equity and Convertible Preferred Stock - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Preferred stock convertible into common stock, ratio	100.00%
Preferred stock mandatory conversion terms, minimum gross proceeds	$ 35,000,000
Preferred stock mandatory conversion terms, minimum price per share	$ 3.50
Dividends declared	$ 0
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, issued		27,777,778
Purchase price per share	$ 1.80	$ 1.80
Gross proceeds		$ 50,000,000
Preferred stock dividend percentage	8.00%
Series C Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, issued	25,232,199
Purchase price per share	$ 3.23
Gross proceeds	$ 81,500,000
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Purchase price per share	$ 0.60
Preferred stock dividend percentage	8.00%
Series A-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Purchase price per share	$ 0.60
Preferred stock dividend percentage	8.00%
Series A-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Purchase price per share	$ 1.20
Preferred stock dividend percentage	8.00%
Series A-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Purchase price per share	$ 1.20
Preferred stock dividend percentage	8.00%

Stockholders' (Deficit) Equit45

Stockholders' (Deficit) Equity and Convertible Preferred Stock - Summary of Convertible Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Shares Authorized	91,543,762	66,311,563
Shares Issued	91,315,295	65,833,096
Shares Outstanding	91,315,295	65,833,096
Carrying Value	$ 165,778	$ 83,702
Liquidation Preference	174,612	$ 89,975
Cumulative Convertible Preferred Stock Dividends	$ 10,829
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	13,470,279
Shares Issued	13,370,279
Shares Outstanding	13,370,279
Issuance Price per Share	$ 0.60
Carrying Value	$ 8,936
Liquidation Preference	9,866
Cumulative Convertible Preferred Stock Dividends	$ 1,844
Series A-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	10,164,552
Shares Issued	10,102,055
Shares Outstanding	10,102,055
Issuance Price per Share	$ 0.60
Carrying Value	$ 6,712
Liquidation Preference	7,348
Cumulative Convertible Preferred Stock Dividends	$ 1,287
Series A-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	5,833,334
Shares Issued	5,833,334
Shares Outstanding	5,833,334
Issuance Price per Share	$ 1.20
Carrying Value	$ 7,287
Liquidation Preference	8,019
Cumulative Convertible Preferred Stock Dividends	$ 1,023
Series A-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	8,780,898
Shares Issued	8,749,650
Shares Outstanding	8,749,650
Issuance Price per Share	$ 1.20
Carrying Value	$ 10,960
Liquidation Preference	12,060
Cumulative Convertible Preferred Stock Dividends	$ 1,566
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	28,062,500
Shares Issued	28,027,778
Shares Outstanding	28,027,778
Issuance Price per Share	$ 1.80	$ 1.80
Carrying Value	$ 50,547
Liquidation Preference	55,165
Cumulative Convertible Preferred Stock Dividends	$ 4,425
Series C Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized	25,232,199
Shares Issued	25,232,199
Shares Outstanding	25,232,199
Issuance Price per Share	$ 3.23
Carrying Value	$ 81,336
Liquidation Preference	82,154
Cumulative Convertible Preferred Stock Dividends	$ 684

Stock Incentive Plan - Addition

Stock Incentive Plan - Additional Information (Detail) $ / shares in Units, $ in Millions	Jan. 30, 2018USD ($)shares	Jan. 31, 2018USD ($)shares	Mar. 31, 2018USD ($)award$ / sharesshares	Mar. 31, 2017$ / shares	Dec. 31, 2017USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of unvested stock options outstanding			2,548,395
Weighted average fair value of options granted | $ / shares			$ 7.91	$ 1.75
Employee and non-employee stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense, stock options | $			$ 8.8
Compensation cost not yet recognized, period for recognition			1 year 10 months 9 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized, period for recognition			1 year 4 months 2 days
Unrecognized stock based compensation expense, restricted stock | $			$ 0.1
Series B Preferred Stock [Member] | Non Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued in exchange for service	250,000	250,000
Fair value of underlying shares | $		$ 0.7
Series B Preferred Stock [Member] | Non Employees [Member] | General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of underlying shares | $	$ 0.7		$ 0.1		$ 0.7
2015 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock reserved for grant			4,462,004
Number of performance-based awards for which vesting is not probable | award			10
Number of common stock available for future grant			1,007,866		107,262
2015 Stock Incentive Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
2015 Stock Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for purchase			980,632
Options granted, maximum expiration period			10 years
2015 Stock Incentive Plan [Member] | Maximum [Member] | Non-Employee Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
2015 Stock Incentive Plan [Member] | Minimum [Member] | Non-Employee Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year

Stock Incentive Plan - Summary

Stock Incentive Plan - Summary of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 652	$ 203
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	410	111
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 242	$ 92

Stock Incentive Plan - Summar48

Stock Incentive Plan - Summary of Stock Option Activity (Detail) - 2015 Stock Incentive Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Number of Shares
Number of Shares, Options outstanding, beginning balance	3,179,536
Number of Shares, Options granted	82,367
Number of Shares, Options exercised	(31,765)
Number of Shares, Options canceled	(2,343)
Number of Shares, Options outstanding, ending balance	3,227,795
Number of Shares, Options Exercisable, end of the period	679,400
Number of Shares, Options vested and expected to vest, end of the period	3,227,795
Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Options outstanding, beginning balance	$ 1.88
Weighted-Average Exercise Price Per Share, Options granted	3.96
Weighted-Average Exercise Price Per Share, Options exercised	1.13
Weighted-Average Exercise Price Per Share, Options canceled	1.12
Weighted-Average Exercise Price Per Share, Options outstanding, ending balance	1.95
Weighted-Average Exercise Price Per Share, Options Exercisable, end of the period	1.07
Weighted-Average Exercise Price Per Share, Options vested and expected to vest, end of the period	$ 1.95
Weighted- Average Remaining Contractual Life
Weighted- Average Remaining Contractual Life, Options outstanding	8 years 9 months 29 days	9 years 18 days
Weighted- Average Remaining Contractual Life, Options Exercisable, end of the period	8 years 3 months 15 days
Weighted- Average Remaining Contractual Life, Options vested and expected to vest, end of the period	8 years 9 months 29 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Options outstanding	$ 27,544		$ 19,803
Aggregate Intrinsic Value, Options Exercisable, end of the period	6,395
Aggregate Intrinsic Value, Options vested and expected to vest, end of the period	$ 27,544

Stock Incentive Plan - Schedule

Stock Incentive Plan - Schedule of Assumptions to Used Determine Fair Value of Options Granted to Employees and Non-employees (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.48%	2.10%
Expected life (in years)	6 years 2 months 1 day	6 years 18 days
Volatility	78.20%	82.90%
Expected dividend rate	0.00%	0.00%
Fair value of common stock	$ 9.67	$ 2.49
Non-Employee Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.53%	2.30%
Expected life (in years)	8 years 9 months 14 days	9 years 3 months 15 days
Volatility	77.90%	82.50%
Expected dividend rate	0.00%	0.00%
Fair value of common stock	$ 10.48	$ 3.06

Stock Incentive Plan - Summar50

Stock Incentive Plan - Summary of Restricted Stock Activity (Detail) - Restricted Stock [Member]	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested Restricted Common Stock, Beginning balance | shares	257,876
Shares, Vested | shares	(31,557)
Unvested Restricted Common Stock , Ending balance | shares	226,319
Unvested Restricted Common Stock, Weighted average price, beginning balance | $ / shares	$ 0.40
Vested, Weighted average price | $ / shares	0.34
Unvested Restricted Common Stock, Weighted average price, ending balance | $ / shares	$ 0.38

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	35.00%
Foreign earnings	$ 0
Provisional amount recorded related to remeasurement of deferred tax balance	$ 11,900,000

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	25,896,792	16,257,697
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	22,386,670	13,892,227
Unvested Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	226,319	387,033
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	56,008	47,496
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	3,227,795	1,930,941

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] $ / shares in Units, $ in Millions	May 11, 2018USD ($)$ / sharesshares	Apr. 27, 2018
Subsequent Event [Line Items]
Reverse stock split ratio		0.2451
Common Stock [Member] | IPO [Member]
Subsequent Event [Line Items]
Number of shares issued in transaction	5,312,500
Public offering price per share | $ / shares	$ 16
Net proceeds from transaction | $	$ 75.9
Conversion of shares, shares converted	22,386,670